1. Field of the Invention
The present invention relates to a cleaning device and an image forming apparatus.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a charged photoconductor with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor (image carrier) on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet, followed by heating and pressurization, whereby an image is formed on the sheet.
In an image forming apparatus of an intermediate transfer belt type and the like, a toner image formed on a photoconductor drum is temporarily transferred to an intermediate transfer belt, and then the toner image transferred on the intermediate transfer belt is transferred to a recording sheet. In this process, the toner is not completely transferred to the recording sheet, and remains on the surface of the intermediate transfer belt. The remaining toner hinders subsequent image forming, and causes a problem that a favorable transfer image cannot be obtained. Under such circumstances, image forming apparatuses are provided with a cleaning device for removing toner.
The cleaning device is provided with a cleaning member that removes the toner on the surface of the intermediate transfer belt. In particular, in image forming apparatuses for use in light-duty printing such as production printing, a large amount of toner is frequently transferred to the intermediate transfer belt. Therefore, it is desirable that, in image forming apparatuses for production printing, the cleaning member have a function for instantly removing a large amount of toner. To ensure such a removing function, cleaning brushes have been used as the cleaning member.
As a technique in which a cleaning brush is used as a cleaning member, a technique has been proposed in which the pre-cleaning brush roller to which a voltage having a polarity opposite to the regular charging polarity of toner is applied so as to electrostatically remove toner having the regular charging polarity is disposed on the upstream of a charging toner cleaning brush roller and an oppositely charging toner cleaning brush roller in a surface-traveling direction of an intermediate transfer belt. Here, the regular charging toner cleaning brush roller electrostatically removes toner having a regular charging polarity, and the oppositely charging toner cleaning brush roller electrostatically removes toner having a polarity opposite to the regular charging polarity (see, for example, Japanese Patent Application Laid-Open No. 2012-88668).
However, in the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2012-88668, depending on the cleaning condition, a function of oppositely charging toner having the regular charging polarity that passes through the pre-cleaning brush roller may be impaired. In this case, disadvantageously, toner that has passed through the pre-cleaning brush roller cannot be sufficiently removed by the regular charging toner cleaning brush roller and the oppositely charging toner cleaning brush roller that are disposed on the downstream of the pre-cleaning brush roller.